We have developed new assays for the functioning of IgG Fc receptors and complement receptors in various groups of patients with immunologic disease. All patients with active lupus erythematosus have major abnormalities in their Fc receptors. Patients with mixed IgM-IgG cryoglobulins, although they have high levels of circulating immune complexes, have no such abnormalities. These patients of course do not usually develop renal disease. Patients with Sjogren's syndrome have been divided into two groups, those with Fc Clearance defects, and those with normal Fc specific clearance. The patients with normal Fc receptor function have disease which is confined to glands of the face and head. Patients with abnormal Fc receptor function have wide-spread illness which includes rheumatoid arthritis, interstitial nephritis, interstitial pulmonary disease, and other signs of extra facial immunologic disorders. The results suggest that this important assay can divide patients with various kinds of immunologic abnormalities into pathophysiologic groups.